The present invention is directed to a carburetor in which a control valve for regulating the flow of exhaust gases to be charged into the carburetor is operatively coupled to the carburetor throttle valve.
One of the best known and effective methods for reducing the nitrogen oxide content in the exhaust gases discharged from an internal combustion engine is the so-called exhaust gas recirculation method in which exhaust gases are returned to the intake system of the carburetor to decrease the maximum combustion temperature and thereby reduce the production of nitrogen oxides. In automotive internal combustion engines, the output from the engine can be controlled in response to the degree of opening of a throttle valve within the carburetor. Accordingly, it is most desirable if a one-to-one relationship between the opening of the throttle valve and the opening of the control valve for regulating the flow rate of the recirculated exhaust gases to be charged into the engine can be established. To accomplish such a relationship, the throttle valve is operatively coupled to the control valve through a linkage arrangement, however, the problem exists that the control valve may be frozen in position when the ambient temperature is extremely low and, further, it often happens that the control valve malfunctions due to corrosion. If the control valve cannot be operated, the operation of the throttle valve for controlling engine output is also adversely affected with the result that the engine cannot be started or the operation of the engine cannot be controlled. Furthermore, there is the problem that when the engine is running under a low load and it is unnecessary to recirculate exhaust gases, the exhaust gases are nonetheless recirculated because the throttle valve is operatively coupled to the control valve.